Plasma generator

Abstract

Discharge can occur from the circumferential area at the tip of the electrode rod, and this discharge can cause localized wear of the electrode rod. [Solution] The plasma generator 1 comprises a metal nozzle 20 having a gas channel 26 through which process gas flows and an outlet 23 from which process gas is discharged from the gas channel 26, and an electrode rod 11 inserted into the gas channel 26 and to which a voltage is applied. The plasma generator 1 has a rotation mechanism 40 that rotates the nozzle 20 around the axis L of the electrode rod 11 as the axis of rotation. A projection 25 is formed on the inner wall surface 26a of the gas channel 26, projecting toward the tip portion 11a of the electrode rod 11.

Description

Technical Field

[0001] The present invention relates to a plasma generator.

Background Art

[0002] As a technology of this kind, for example, Patent Document 1 discloses a plasma generator (plasma torch) including a nozzle in which a gas flow path is formed and an electrode rod disposed in the gas flow path. When generating plasma, a voltage is applied between the electrode rod and the nozzle, so that a discharge occurs between them, and a part of the process gas is made into plasma (activated). In this plasma generator, by attaching a columnar insulating guide having spiral grooves to the electrode rod, a swirling flow is generated in the process gas flowing toward the tip portion of the electrode rod. As a result, a thin cooling gas layer is formed on the inner peripheral surface of the nozzle, suppressing the temperature rise of the inner wall of the nozzle.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the plasma generator disclosed in Patent Document 1, the swirling flow of the process gas reaching the tip portion of the electrode rod is not sufficient, and discharge may occur from a specific location in the circumferential direction of the tip portion of the electrode rod, and the electrode rod may be locally consumed by this discharge.

[0005] The present invention has been made in view of such points, and an object thereof is to provide a plasma generator capable of suppressing local consumption of an electrode rod.

Means for Solving the Problems

[0006] In view of the above problems, the plasma generator according to the present invention comprises a metal nozzle having a gas channel through which a process gas flows and an outlet from which the process gas containing plasma is discharged from the gas channel, and an electrode rod inserted into the gas channel and to which a voltage for plasma generation is applied between the electrode rod and the nozzle, wherein the plasma generator has a rotation mechanism that rotates the nozzle with the axis of rotation being the axis of rotation of the electrode rod, and a projection is formed on the inner wall surface of the gas channel that protrudes toward the tip of the electrode rod.

[0007] According to the present invention, a discharge can be generated by applying a voltage between a projection formed on the inner wall surface of the nozzle and the tip of the electrode rod, thereby plasmaizing a portion of the process gas flowing between them. Here, since the nozzle rotates around the axis of the electrode rod by a rotation mechanism, the projection formed on the inner wall surface of the gas flow path also orbits around the tip of the electrode rod. This makes it possible to avoid discharge from a specific point in the circumferential direction of the tip of the electrode rod, and to suppress localized consumption of the electrode rod due to this discharge.

[0008] In a more preferred embodiment, the gas flow path has a throttling space formed therein, the flow path cross-section of which narrows as it proceeds toward the outlet side, the throttling space having a base end located upstream of the process gas and a tip located downstream of the process gas along the direction of the axis, and the protrusion is formed at least adjacent to the base end.

[0009] According to this embodiment, since the protrusion is formed adjacent to the base end of the diaphragm space, the end of the protrusion can be moved over a larger radius as the nozzle rotates around the axis, compared to the case where the protrusion is positioned adjacent to the tip of the diaphragm space. As a result, discharge can be performed over a wider area of ​​the surface of the tip of the electrode rod.

[0010] In a more preferred embodiment, the protrusion is formed continuously from the base end to the tip end of the diaphragm space, and the height from the inner wall surface forming the diaphragm space decreases as it progresses from the base end to the tip end of the diaphragm space.

[0011] In this embodiment, a discharge occurs at the tip of the protrusion on the base end side of the diaphragm space, causing a portion of the process gas to be converted into plasma and generating plasma. Here, the protrusion, which is continuous from the base end to the tip of the diaphragm space, acts as a vane that swirls the process gas (process gas containing plasma) in the diaphragm space. This allows the plasma-containing gas passing through the diaphragm space to swirl. As a result, the emitted plasma can be sent further away from the nozzle tip.

[0012] In a more preferred embodiment, the throttling space is a space having the shape of a frustocone, and the inner wall surface forming the throttling space is inclined with respect to the generatrix of the frustocone such that the protrusion is inclined with respect to the generatrix of the frustocone such that a swirling flow of the process gas is formed in the same direction as the rotation direction of the nozzle.

[0013] According to this embodiment, the protrusions on the inner wall surface forming the throttling space are inclined with respect to the generatrix of the frustocone so that the process gas containing plasma swirls in the same direction as the rotation direction of the nozzle, thereby improving the swirling ability of the process gas containing plasma in the throttling space. As a result, the emitted plasma can be sent even further away from the tip of the nozzle.

[0014] Of the aforementioned protrusions, a chamfered surface is formed on the end facing the tip portion of the electrode rod.

[0015] According to this embodiment, if the tip of the projection formed on the inner wall surface of the nozzle is sharp, discharge is likely to occur at a specific position on the tip of the electrode rod. However, since a chamfered surface is formed on the tip of the projection, the sharpness of the tip is eliminated, and localized discharge at the end of the projection can be suppressed. [Effects of the Invention]

[0016] According to the present invention, localized consumption of the electrode rod can be suppressed. [Brief explanation of the drawing]

[0017] [Figure 1] This is an exploded perspective view of a plasma generator according to an embodiment of the present invention, with the cover removed. [Figure 2] (a) is a perspective view of the nozzle tip shown in Figure 1, viewed from below; (b) is a perspective view of the nozzle tip, viewed from above; (c) is a top view of the nozzle tip; and (d) is a cross-sectional view of the nozzle tip. [Figure 3] Figure 1 is a cross-sectional view of the main part of the plasma generator. [Figure 4] (a) is a cross-sectional view showing a modified example of the plasma generator nozzle, and (b) is a cross-sectional view showing another modified example of the plasma generator nozzle. [Modes for carrying out the invention]

[0018] A plasma generator 1 according to an embodiment of the present invention will be described below with reference to Figures 1 to 4. The plasma generator 1 generates plasma from a portion of the supplied process gas by applying a plasma generation voltage V between a nozzle 20 supplied with process gas and an electrode rod 11 inserted into the nozzle 20, thereby causing a discharge between the electrode rod 11 and the nozzle 20. The generated plasma is then discharged from an outlet 23.

[0019] Examples of the discharge between the electrode rod 11 and the nozzle 20 include arc discharge, streamer discharge, glow discharge, etc. As long as plasma can be generated, the form of the discharge is not particularly limited. The type of discharge can be set according to the type of process gas and the conditions of the applied voltage (such as the magnitude of the voltage and the shape of the voltage waveform). In this specification, since a part of the process gas becomes plasma, the process gas containing plasma may sometimes be referred to as plasma hereinafter.

[0020] In such a plasma generator 1, a part of the process gas (for example, O2, etc.) flowing from the upstream is ionized to generate plasma. The process gas containing the generated plasma is sprayed, and a predetermined treatment is performed with the sprayed plasma. For example, surface modification of a metal member or the like is performed using plasma. Of course, it can also be used for other applications.

[0021] As shown in FIG. 3, the electrode rod 11 is, for example, a rod-shaped metal member mainly made of copper. The electrode rod 11 is inserted into the gas flow path 26 of the nozzle 20 to be described later in a non-contact state with the nozzle 20, and a voltage V is applied between the electrode rod 11 and the nozzle 20. The tip portion 11a of the electrode rod 11 may have a conical or frustum shape, but in this embodiment, it has a hemispherical surface. Thereby, the surface of the tip portion 11a of the electrode rod 11 becomes a rounded surface, so that discharge from a specific position of the tip portion 11a of the electrode rod 11 can be suppressed.

[0022] The base end of the electrode rod 11 is attached to an electrode holder (not shown) made of metal such as copper, and the electric wire 71 shown in FIG. 1 is attached to the electrode holder. Thereby, the voltage V (specifically, a voltage with a pulse waveform) from a power source (not shown) connected to the electric wire 71 can be supplied to the electrode rod 11.

[0023] Furthermore, a columnar flow straightening member 12, having multiple spiral grooves 12a formed on its outer surface, is attached to the electrode rod 11. The flow straightening member 12 is a member that straightens the process gas so that the process gas traveling linearly along the gas flow path 26 forms a swirling flow, and is inserted into the internal space 31a of the cylindrical body 31, which will be described later. Due to the grooves 12a formed on the outer surface of the flow straightening member 12, the process gas that passes through the grooves 12a forms a swirling flow F downstream of the flow straightening member 12. The grooves 12a are formed so that the direction of the swirling flow of the process gas that passes through the flow straightening member 12 is the same as the rotation direction R of the nozzle 20, which will be described later.

[0024] As shown in Figure 3, the plasma generator 1 comprises at least a metal nozzle 20 and an electrode rod 11. The nozzle 20 has a gas channel 26 through which process gas flows and an outlet 23 from which process gas containing plasma is discharged from the gas channel 26. The nozzle 20 is connected to earth and comprises a cylindrical nozzle body 21 and a nozzle tip 22 screwed onto the tip of the nozzle body 21. The upstream structure of the gas channel 26 is not shown in the figure, but it is connected to a gas supply pipe 72.

[0025] In this embodiment, the nozzle body 21 is a cylindrical body having a large diameter portion 21a and a small diameter portion 21b, and a ring gear 44 is attached to the large diameter portion 21a. A nozzle tip 22 is attached to the tip side of the small diameter portion 21b so that a gas flow path 26 is formed along the axis L of the electrode rod 11 that is inserted. In this embodiment, the nozzle 20 is composed of a nozzle body 21 and a nozzle tip 22, but the nozzle body 21 and the nozzle tip 22 may be integrally molded as long as the electrode rod 11 and a cylindrical body 31, etc., described later can be inserted.

[0026] In this embodiment, a cylindrical body 31 made of an insulating material such as ceramics (e.g., alumina) is inserted into the gas flow path 26 along the axis L of the electrode rod 11 and covering the electrode rod 11. The internal space 31a of the cylindrical body 31 becomes part of the gas flow path 26 of the nozzle 20.

[0027] As shown in Figure 1, the plasma generator 1 has a rotation mechanism 40 that rotates the nozzle 20 around the axis L of the electrode rod 11. The rotation mechanism 40 is equipped with a motor 41, and a pinion gear 43 is attached to the output shaft 42 of the motor 41. The pinion gear 43 meshes with a ring gear 44 fixed to the nozzle body 21. The casing 29 is fixed to external equipment (not shown) and also fixed to the electrode rod 11 via internal components (not shown), and the internal components and the electrode rod 11 are rotatable via bearings. As a result, when the motor 41 is driven, the nozzle 20 can be rotated relative to the electrode rod 11, with the axis L of the electrode rod 11 as the axis of rotation.

[0028] As shown in Figures 2(a) and 2(b), the nozzle tip 22 has a screw groove (not shown) formed on its outer surface 22b and a seal groove 22c. As shown in Figure 3, an O-ring 83 is placed in the seal groove 22c, and the nozzle tip 22 is screwed to the nozzle body 21 by screwing the screw groove of the nozzle tip 22 into the nozzle body 21. The nozzle tip 22 has an opening 27 into which the tip of a cylindrical body 31 made of insulating material is inserted. The cylindrical body 31 is inserted from the opening 27 along the inner circumferential surface 22d continuous with the opening 27 until the end face 31b of the cylindrical body 31 abuts against the ring-shaped bottom surface 22e of the nozzle tip 22 (see Figure 2(d)). An outlet 23 is formed at a position corresponding to the tip 22a of the nozzle tip 22 (the tip 20a of the nozzle 20) from which process gas containing plasma is released.

[0029] As shown in Figures 2(c) and 2(d), a throttling space 26A is formed in the gas flow path 26 of the nozzle tip 22, where the flow path cross-section narrows as it proceeds toward the discharge port 23. The throttling space 26A is a space with the shape of a frustocone. The throttling space 26A has a base end portion 26f located upstream of the process gas along the axis L of the electrode rod 11, and a tip portion 26c located downstream of the process gas. Between the tip portion 26c of the throttling space 26A and the discharge port 23, a cylindrical communication space 26B is formed along the axis L of the electrode rod 11, connecting the throttling space 26A and the discharge port 23. The communication space 26B is a cylindrical space formed by the inner wall surface 26b.

[0030] The inner wall surface 26b forming the communication space 26B may have spiral grooves formed in the same direction as the swirling flow F of the process gas formed by the flow straightening member 12, so that the swirling flow F is formed in the same direction. This allows the process gas containing plasma (plasma-treated gas) to be discharged from the outlet 23 with the swirling flow F formed in the rotational direction of the nozzle 20, and the discharged plasma can be sent further away from the tip of the nozzle.

[0031] In this embodiment, the communication space 26B is formed in a direction along the axis L of the electrode rod 11. However, for example, as shown in Figure 2(d), the communication space 26C may be formed along a virtual line L2 that intersects the axis L. In this case, since the discharge port 23A is formed at the position shown in Figure 2(a), rotating the nozzle 20 around the axis L allows the process gas discharged from the discharge port 23A to be blown over a wider area.

[0032] In this embodiment, a projection 25 is formed on the inner wall surface 26a of the throttling space 26A of the gas flow path 26, projecting toward the tip portion 11a of the electrode rod 11. The projection 25 is formed adjacent to the base end portion 26f. As shown in Figure 2(d), the projection 25 has an upper end surface 25b extending toward the axis L and a side surface 25c parallel to the axis L. As a result, the height of the projection 25 from the inner wall surface 26a forming the throttling space 26A decreases as it progresses from the base end portion 26f to the tip portion 26c of the throttling space 26A. At the boundary between the upper end surface 25b and the side surface 25c, there is an end facing the tip portion 11a of the electrode rod 11, and a chamfered surface 25a is formed at this end.

[0033] According to this embodiment, a discharge can be generated by applying a voltage between the protrusion 25 formed on the inner wall surface 26a of the nozzle 20 and the tip portion 11a of the electrode rod 11, thereby plasmaizing a portion of the process gas flowing between them.

[0034] Here, the nozzle 20 rotates around the axis L of the electrode rod 11 by the rotation mechanism 40, so the protrusion 25 formed on the inner wall surface 26a of the gas flow path 26 also orbits around the tip portion 11a of the electrode rod 11. This prevents discharge from specific points in the circumferential direction of the tip portion 11a of the electrode rod 11, and suppresses localized consumption of the electrode rod 11 due to such discharge. Furthermore, due to such discharge, a portion of the process gas becomes plasma, and the process gas containing the plasma can be discharged from the outlet 23.

[0035] Furthermore, since the projection 25 is formed adjacent to the base end 26f of the diaphragm space 26A, compared to the case where the projection 25 is positioned adjacent to the tip end 26c of the diaphragm space 26A, the tip of the projection 25 (in this embodiment, the chamfered surface 25a) can be moved over a larger radius as the nozzle 20 rotates around its axis. As a result, discharge can be performed over a wider area of ​​the surface of the tip portion 11a of the electrode rod 11.

[0036] Furthermore, if the tip of the projection 25 formed on the inner wall surface 26a of the nozzle 20 is sharp, discharge is likely to occur at a specific position on the tip portion 11a of the electrode rod 11. By forming a chamfered surface 25a on the tip of the projection 25, the sharpness of the tip is eliminated, and localized discharge at the end of the projection 25 can be suppressed.

[0037] Figure 4(a) is a cross-sectional view showing a modified example of the nozzle of the plasma generator. As shown in this modified example in Figure 4(a), the projection 25A may be formed continuously from the base end 26f to the tip end 26c of the throttling space 26A. The height of the projection 25 from the inner wall surface 26a forming the throttling space 26A decreases as it progresses from the base end 26f to the tip end 26c of the throttling space 26A.

[0038] In this modified version, a discharge occurs at the tip (chamfered surface 25a) of the projection 25A on the base end 26f side of the diaphragm space 26A, generating plasma. Furthermore, the projection 25A, which extends continuously from the base end 26f to the tip end 26c of the diaphragm space 26A, acts as a vane that swirls the process gas (process gas containing plasma) in the diaphragm space 26A. This allows the process gas (process gas containing plasma) to swirl within the diaphragm space 26A. As a result, the emitted plasma can be sent further away from the nozzle tip.

[0039] Figure 4(b) is a cross-sectional view showing another modified example of the plasma generator nozzle. As shown in Figure 4(b), the projection 25B may be inclined with respect to the generatrix of the frustocone so that the plasma can easily swirl in the same direction as the rotational direction R of the nozzle 20. In other words, in this example, the projection 25B is formed in a helical shape so that the process gas (process gas containing plasma) can swirl more easily. This improves the swirling ability of the process gas containing plasma in the throttling space 26A. As a result, the emitted plasma can be sent further away from the tip 20a of the nozzle 20.

[0040] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various design modifications can be made without departing from the spirit of the invention as described in the claims. [Explanation of Symbols]

[0041] 1: Plasma generator, 11: Electrode rod, 11a: Tip section, 20: Nozzle, 23: Discharge port, 25, 25A, 25B: Protrusions, 25a: Chamfered surface, 26: Gas flow path, 26A: Throttle space, F: Swirling flow, L: Axis center

Claims

1. A metal nozzle having a gas channel through which a process gas flows, and an outlet from which the process gas containing plasma is discharged from the gas channel, A plasma generator comprising an electrode rod inserted into the gas flow path and to which a voltage for plasma generation is applied between the nozzle, The plasma generator has a rotation mechanism that rotates the nozzle around the axis of rotation of the electrode rod, A plasma generator characterized in that a protrusion is formed on the inner wall surface of the gas flow path, which protrudes toward the tip of the electrode rod.

2. The gas flow path has a constricted space formed in which the cross-sectional area of ​​the flow path narrows as it proceeds toward the outlet side. The throttling space has a base portion located upstream of the process gas and a tip portion located downstream of the process gas, along the direction of the axis. The plasma generator according to 1, characterized in that the protruding portion is formed at least adjacent to the base end.

3. The aforementioned protrusion is formed continuously from the base end to the tip end of the constricted space, The plasma generator according to claim 2, characterized in that the height from the inner wall surface forming the throttling space decreases as the throttling space progresses from the base end to the tip end.

4. The aforementioned aperture space is a space having the shape of a truncated cone, The plasma generator according to claim 3, characterized in that the inner wall surface forming the throttling space is inclined with respect to the generatrix of the frustum in the same direction as the rotation direction of the nozzle, such that a swirling flow of the process gas is formed.

5. The plasma generator according to claim 1, characterized in that a chamfered surface is formed on the end of the protruding portion that faces the tip portion of the electrode rod.

Images